Determination of methylation status of the MDR1promoter region by quantitative PCR analysis. Genomic DNA isolated from either NPB (A, B, D, E) or KB 3-1 cell line (C, F) was digested withPst I (A, D), Msp I/Pst I (B, E), orHpa II/Pst I (C, F), respectively, serially diluted, and amplified by PCR. (A, B, and C) The ethidium bromide stain after electrophoresis of PCR products in a 2% agarose gel. The gel was analyzed with NIH image, and plotted as a graph (D, E, F). The corresponding region and size of PCR products for the primer pairs MM2, MM4, MC2, and TPI5 were the MDR1 promoter containing MspI/Hpa II sites (Fig 1) and 121 bp; MDR1 promoter containing Msp I/Hpa II sites (Fig 1), 206 bp;MDR1 promoter containing no Msp I/Hpa II site (Fig 1), 240 bp; and triosephosphate isomerase gene promoter containingMsp I/Hpa II sites, 240 bp, respectively. The results for PCR primer pairs MM2, MM4, MC2, and TPI5 were plotted by (◊), (○), (□), and (•), respectively.